The present invention relates to an electromagnetic relay, and more particularly relates to an electromagnetic relay in which switch contacts are switched over by movement of an armature assembly in response to the energization of an electromagnet, in which it is practicable to obtain a good switching characteristic for the relay.
There is a known type of electromagnetic relay, comprising an electromagnet which may comprise an electromagnetic coil with an iron core, and a movable block equipped with an an armature which is positioned opposed to said electromagnet. The movable block is mounted so as to be reciprocable to and fro, according to the magnetization or demagnetization of the electromagnet, and contacts are provided which are opened and closed according to this reciprocal movement of said movable block. Thus, when the electromagnet is energized, the movable block is biased in a certain direction, and moves so as to open or close certain of the contacts. On the other hand, when the coil is energized in the electrical direction opposite to said particular direction, the movable block is biased in the opposite direction, and moves so as to close or open said certain of its contacts. (The position when the coil is not energized can be either of these positions or a position intermediate between them, depending on the biasing of the movable block). Thereby the contacts are reliably and positively switched, and a good and efficient relay is provided.
An important question that arises in the design and production of an electromagnetic relay is the importance of adjusting the biasing force characteristics of the armature assembly thereof. As schematically illustrated in FIG. 4 of the accompanying drawings, which shows various forces on the armature assembly along the vertical axis and the displacement of said armature assembly along the horizontal axis, it is desirable that, in all positions of the armature assembly, the biasing force on the armature should be between the actuation force on said armature assembly and the required restoring force for said armature assembly. In other words, the amount of force available for moving said armature, when the relay is actuated, should be greater than the biasing force on the armature assembly, so that the armature assembly can reliably be moved for actuation; while on the other hand this biasing force on the armature assembly should be greater than the required force for restoring the armature assembly, so that the armature assembly can reliably be restored to its original position, when so required. When this condition is considered for all positions of the armature assembly, we derive the condition that the biasing force curve for the armature assembly, illustrated by the curve (B) in FIG. 4, should fall between the actuation force curve, illustrated by the curve (A) in FIG. 4 and based on the voltage applied to the coil of the relay, and the required restoring force curve, illustrated by the curve (C) in FIG. 4. However, in the past the adjustment of the biasing force characteristic curve of an electromagnetic relay of this type has been performed by adjusting a single sheet spring which is used for restoring the armature, and this makes it difficult to rigorously adapt the biasing force characteristics of the armature to more rigorous requirements. Furthermore, due to fluctuations in the mechanical characteristics of the parts inevitably caused by manufacturing tolerances, and due to assembly inaccuracies, the biasing force characteristic curve may depart from the desired one to some extent. In short, if only one sheet spring is used for restoring the position of the armature assembly then it is very difficult to properly fine adjust the operational characteristics of the relay.
Further, an important point is to prevent any woggling or swaying of the armature assembly during its motion, i.e. to preserve its self parallelism as it is reciprocated by selective energization of the electromagnet assembly. Such woggling or snaking motion of the armature assembly can cause some delay in the contact action thereof, and some unevenness in operational performance of the relay, and further can cause different portions of the contact assembly to come into contact with other different portions, thereby causing uncertain operation. In the case that the contact portions of the contact assembly are covered with or are made of a precious metal such as gold, either this will result in some non gold portions coming into mutual contact for electrical conduction, which will nullify the benefits of using gold at all and will mean that the resistance of the relay contacts is variable and unpredicable, or alternatively it will be necessary to use a larger quantity of the precious metal, which is expensive. Further, mutual sliding and mutual fretting can be caused between the relay contacts by such inclined or woggling motion of the armature assembly as it moves, and this can cause undue wear on these contacts. Especially, this swaying of the armature assembly can be caused by asymmetry in its biasing means, although in fact the armature assembly is not immune to swaying and canting if its biasing means is symmetrically arranged. Accordingly it is important to provide a sure and positive means for preventing swaying and canting of the armature assembly.